Diagnosis and treatment of conditions affecting the brain are among the most difficult and complex problems that face the medical profession. The brain is a complex and delicate soft multi-component tissue structure that controls bodily functions through a complex neural network connected to the rest of the body through the spinal cord. The brain and spinal cord are contained within and protected by significant bony structures, e.g., the skull and the spine. Given the difficulty of accessing the brain through the hard bony protective skull and the delicate network and complex interactions that form the neural communication network contained within the brain that define the human body's ability to carry on its functions of speech, sight, hearing, functional mobility, reasoning, emotions, respiration and other metabolic functions, the diagnosis and treatment of brain disorders presents unique challenges not encountered elsewhere in the body.
For example, abnormalities such as intracranial cerebral hematomas (ICH), abscesses, glioblastomas (GB), metastases (mets) and functional diseases manifest themselves in the intraparenchymal subcortical space (i.e., the white matter) of the brain are particularly challenging to access, let alone treat. The hemispheres [jm1] of the brain contain eloquent communication structures (neural network) which are located in the subcortical space, called fiber tracts and fascicles. Thus, traditionally, unless the ICH, GB, and/or mets were considered anything but “superficial,” such conditions have been considered challenging to access, simply because getting to the abnormality ICH, GB and/or mets are considered just as damaging as letting the condition take its course. Similarly, tissue abnormalities such as tumors, cysts and fibrous membrane growths which manifest within the intraventricular space of the brain are considered challenging to safely access and often inoperable, due to their locations within the brain.
In order to assist in diagnosis and subsequent treatment of brain disorders, clear, accurate imaging of brain tissue through the skull is required. In recent years significant advances have been made in imaging technology, including stereotactic X-ray imaging, Computerized Axial Tomography (CAT), Computerized Tomographic Angiography (CTA), Position Emission Tomography (PET) and Magnetic Resonance Imaging (MRI), Diffusion Tensor Imaging (DTI) and Navigation systems (instrument position tracking systems). These imaging devices and techniques permit the surgeon to observe conditions within the brain in a non-invasive manner without opening the skull, as well as provide a map of critical structures surrounding an area of interest, including structures such as blood vessels, membranes, tumor margins, cranial nerves, including fiber tracts and fascicles. If an abnormality is identified through the use of one or more imaging modalities and/or techniques, it may be necessary or desirable to biopsy or remove the abnormality.
Once a course of action has been determined based upon one or more imaging techniques, a surgical treatment may be necessary or desired. In order to operate surgically on the brain, access must be obtained through the skull and delicate brain tissue containing blood vessels and nerves that can be adversely affected by even slight disturbances. Therefore, great care must be taken in operating on the brain so as not to disturb delicate blood vessels and nerves to prevent adverse consequences resulting from a surgical intervention.
Traditionally, accessing abnormalities which manifest in deeper spaces within the brain has meant a need for a surgery that creates a highly invasive approach. In some instances, in order to obtain access to target tissue, a substantial portion of the skull is removed and entire sections of the brain are retracted to obtain access. Such technique is referred to as an “open” procedure. For example, traditional surgical brain retractors are metal bands, with abrupt or well-defined edges and have limited surface areas. These traditional surgical brain retractors are used to pull apart or spread delicate brain tissue, which can leave pressure marks from lateral edges of the retractor, indicating high local compression stress. In some instances, a complication known as “retraction injury” may occur due to use of brain retractors. Further, brain tissue can be torn by the relatively sharp edges of the retractors. In addition, the retracted brain tissue can lose blood supply if the localized pressure of the retractors is greater than the venous pressure, which can lead to ischemic changes. Of course, such “open” techniques are not appropriate for all situations, and not all patients are able to tolerate and recover from such invasive techniques.
It is also known to access certain portions of the brain by creating a burr hole craniotomy, but only limited surgical techniques may be performed through such smaller openings. In addition, some techniques have been developed to enter through the nasal passages, opening an access hole through the occipital bone to remove tumors located, for example, in the area of the pituitary.
A significant advance in brain surgery is stereotactic surgery involving a stereotactic frame correlated to stereotactic X-ray images to guide a navigational system probe or other surgical instrument through an opening formed in the skull through brain tissue to a target lesion or other body. A related advance is frameless image guidance, in which an image of the surgical instrument is superimposed on a pre-operative image to demonstrate the location of the instrument to the surgeon and trajectory of further movement of the probe or instrument. However, once the navigational system probe is removed, information concerning the location of any retractors or other surgical instruments that may be used during procedures is unavailable.
In recent years, surgical access systems have been developed to provide access to previously difficult to access areas. One such prior art system is shown in FIGS. 1A-1C. System 10 includes a retractor 20 and an introducer 40. Retractor 20 has a hollow working channel and is generally shorter than introducer 40. Retractor 20 is configured as a hollow elliptical rounded wedge. Introducer 40 is also hollow and includes a cone-shaped distal end 42 with an opening 52 therein (best seen in FIG. 1C). The cone-shaped distal end is configured to be a generally blunt, flat surface. With introducer 40 positioned within retractor 10, system 10 is inserted into brain tissue, thereby pushing brain tissue away while providing access to an area of interest. Once system 10 is delivered to the area of interest, retractor 10 is rigidly fixed in position. More specifically, retractor 10 is fixed in space with the use of a standard or conventional neurosurgical fixation device. Once retractor 10 is fixed in place, introducer 40 is then removed from retractor 10, while leaving retractor 10 in its fixed place, thereby creating a pathway through the brain tissue. However, no mechanism for providing navigational information concerning the retractor 10 with respect to the patient's anatomy is provided.
While access system 10 may provide a manner to access certain brain tissue, however due the blunt nature of the tip configuration of the inner sheath the cortex must first be opened via a cortisectomy or corticotomy with the use of knife which is traumatic to the cortex and requires the removal of blood vessels on the cortex which provide both the cortex with nutrients and drainage for the elimination of waste products. This is also true of the underlying white matter, which must also be cut to create a space for the device to be inserted, so as to not displace the white matter and cause brain shift or pressure via restrictions on the surrounding eloquent fiber tracts. Therefore, if an opening and pathway are not created for the blunt shaped distal end of the device, it can actually cause transient or even permanent deformation and trauma of delicate tissue structures which can manifest itself in temporary or permanent neurological deficits after surgical cytoreduction due to damage of blood vessels, cranial nerves, fiber tracts and fascicles. Opening 52 may cause coring of tissue, also leading to damage of the tissues and structures as introducer 40 is pushed through tissue. Further, by rigidly fixing the placement of retractor 10, manipulation of retractor 10 is impeded and requires constant attention by loosening and retightening to re-position for even micro-movement of the retractor 10, without critical information concerning surrounding structures in relation to the retractor 10 available, thereby lengthening procedure time.
Thus, there exists a need for improved surgical access system that reduces potential damage to brain tissue and structures, as well as providing navigational capabilities for the access system.